Mechanical pencils of the push-push or knock type as they are known in the writing instrument industry have employed a snap ring disposed in an annular groove near the front end of the lead feed mechanism to retain the reservoir and feed mechanism in its rearwardmost position with the ring being pressed against the front end of the barrel by a coil spring mounted within the barrel in compression between a rearwardly facing shoulder on the barrel and a forewardly facing shoulder on the reservoir and feed mechanism. Pencils of this type have been marketed by the assignee of the present invention, but they have sometimes become inadvertently disassembled because of accidental dislodgement of the snap ring. One cause of this dislodgement of the ring has been its tendency to twist in the annular groove in which it is retained and pop out of the groove.